Re: [Xen-devel] [PATCH 1/5] tools/xc_restore: Initialise console and store mfns

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/11/13 12:12, Ian Jackson wrote:
> Andrew Cooper writes ("[PATCH 1/5] tools/xc_restore: Initialise console and 
> store mfns"):
>> If the console or store mfn chunks are not present in the migration stream,
>> stack junk gets reported for the mfns.
>>
>> XenServer had a very hard to track down VM corruption issue caused by exactly
>> this issue.  Xenconsoled would connect to a junk mfn and incremented the ring
>> pointer if the junk happend to look like a valid gfn.
> A question that arises here is this:
>
> How come this was going undetected ?
>
> If the junk mfn _doesn't_ look like a valid gfn (which presumably it
> mostly doesn't), surely this generates some error message somewhere
> (even if it only causes the console not to work) ?
>
> Ian.

This was a XenServer optimisation to avoid allocating an event channel
in dom0 for hvm domains which wouldn't be using it anyway.  We only
officially support Windows hvm domains, so this is a blanket change for
all hvm domains.

We were not expecting any hvm consoles to work in the slightest, and
xenconsoled gave no hint of errors.

~Andrew

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